The provision of lubrication oil to the main journal bearings and connector rod bearings of a crankshaft is critical to the operation of internal combustion engines. As well as lubricating the relative movement of connected components to reduce wear, oil provides an important cooling function.
Known engines incorporate passageways internal to the engine block through which oil is pumped into main journal bearings of the crankshaft, and internal passageways are provided within the crankshaft between main journal bearings and one, or at most two, adjacent connector rod bearings. The oil flow to the crankshaft bearings is firstly supplied to the main journal bearings from an oil gallery of the engine block, and thence from the main journal bearing to an adjacent connector rod bearing (big end bearing). The oil supply to the oil gallery supplying the main bearings is provided by an oil pump in the engine. Typically the oil is supplied to grooved bearing shells situated in the engine block, whilst the corresponding bearing shells situated in the bearing caps are plain, un-grooved bearing shells. The grooved bearing shell halves are each provided with an oil access hole corresponding in position to the oil supply passageway from the oil supply gallery and a groove around the inner periphery to provide oil into the inputs of the crankshaft's internal passageways to the one or more adjacent connector rod bearings. Disadvantageously, oil pumps for pumping oil into the lubrication system are heavy, bulky, and consume a large amount of energy. Further, the grooved bearing shell that is required at each main journal bearing leaks more oil than a plain bearing shell, increasing oil flow and the necessary pumping rate and power consumption of the oil pump.
Engines having known bearing arrangements are disclosed in JP07027127A and U.S. Pat. No. 7,281,854B2.
JP07027127A discloses crankshaft lubrication arrangements in which main journal bearings are fed with oil by oil supply passageways internal to the engine block, and the connector rod bearings are each fed with oil from main journal bearings through internal passageways of the crankshaft.
In a first arrangement of JP07027127A, an internal oil feed passageway leads from each of the main journal bearings on either side of each connector rod bearing to the respective connector rod bearing. One half of each of the main journal bearings has a semi-cylindrical bearing shell with a semi-cylindrical groove into which oil is pumped through an internal passageway of the engine block, and from which oil is fed into an internal passageway to a connector rod bearing. In this arrangement, alternate main journal bearings alternately have such semi-cylindrical grooves provided in their upper and lower semi-cylindrical bearing shells, and oil is fed to each connector rod bearing from the two adjacent main journal bearings during alternating halves of a complete rotation of the crankshaft.
Disadvantageously, this first arrangement requires every main journal bearing to be provided with a semi-cylindrical bearing shell with a semi-cylindrical groove. Such bearing shells are more expensive than plain bearing shells and leak more oil. For example, in the case of a four cylinder engine according to this design, each of the five main journal bearings requires to be provided with such a bearing shell.
Further, disadvantageously, this first arrangement requires an oil supply passageway to each main journal bearing to be provided in the engine block. The provision of such oil supply passageways in the engine block increases the complexity and manufacturing cost of the engine block. For example, in the case of a four cylinder engine according to this design, having five main journal bearings, five oil supply passageways are required in the engine block.
In a second arrangement of JP07027127A, two internal oil feed passageways lead from alternate main journal bearings to feed oil to the connector rod bearings. One internal passageway leads to each of the connector rod bearings on either side of each of the oil feeding main journal bearings. Again, each of the oil feeding main journal bearings has a semi-cylindrical bearing shell with a semi-cylindrical groove into which oil is pumped through an internal passageways of the engine block. However, both the oil feeding main journal bearings and those main journal bearings that do not feed oil into internal passageways of the crankshaft require to be supplied with oil by oil supply passageways from the oil gallery to provide lubrication.
In this second arrangement, the number of oil feeding main journal bearings is lower than in the first arrangement. However, disadvantageously, in this second arrangement, it is still required that approximately half of the main journal bearings are oil feeding main journal bearings, each of which has a corresponding semi-cylindrical bearing shell with a semi-cylindrical groove. For example, in a four cylinder engine, at least two of the five main journal bearings require to be oil feeding main journal bearings having such a grooved bearing shell, and to be fed through five oil supply passageways in the engine block. In a further example in an engine having six cylinders served by a common crankshaft, at least three of the seven main journal bearings require to be oil feeding main journal bearings having such a grooved bearing shell, and to have seven oil supply passageways.
Further, disadvantageously, this second arrangement still requires an oil supply passageway to be provided in the engine block to each main journal bearing (both the oil feeding main journal bearings and the non-oil feeding main journal bearings). For example, for a four cylinder engine, an oil supply passageway is required for each of the five main journal bearings. Similarly, in an engine having six cylinders served by a common crankshaft, an oil supply passageway is required for each of the seven main journal bearings.
U.S. Pat. No. 7,281,854B2 discloses an engine lubrication arrangement similar to the second arrangement of JP07027127A, described above.
A cross-sectional view of part of a known engine is shown, having several bearing arrangements, is shown in FIG. 1A, with the cross-sectional view being coplanar with the axis of rotation of a crankshaft within the bearing arrangements. The crankshaft 100 has main journal bearing sections 102A to 102C, connector rod bearing sections 104A and 104B, web sections 106, a crankshaft end portion 108, and an oil feed passageways 110. Also shown are corresponding plain bearing shells 112 and a grooved bearing shell 114, which line the bearing housings (bearing shell receiving elements) 117 and 121 of the engine block and cylinder head respectively, and an oil supply passageway 116 within the engine block bearing housing.
The plain bearing shells 112 are concave and substantially semi-cylindrical such that their inner surfaces mate with the bearing surfaces of the main journal bearing sections 102A to 102C. The concave grooved bearing shell 114 is illustrated in FIG. 1B and differs from a plain bearing shell 112 by inclusion of a semi-cylindrical groove 118 on the inner surface and a supply hole 119, which communicates between the groove 118 and the oil supply passageway 116 of the bearing housing 117 of the engine block, such that oil supplied through the oil supply passageway is received into a chamber formed between the groove and the surface of the main journal bearing section 102A.
The oil feed passageways 110 have interconnecting straight bores formed in different sections 102, 104 and 106 of the crankshaft 100. The oil feed passageways 110 each have one inlet 122 and two outlets 124. The inlet 122 is in a first side of a main journal bearing surface 102B and 102C. The first outlet is in an opposite side of corresponding main journal bearing surface 102B an 102C, and a second outlet is in the surface of a connector rod bearing section 104A and 104B. In the case that the crankshaft is formed by assembly of separate sections, the straight bores may be conveniently bored into the sections before assembly.
The oil enters the inlet 122 at a pressure sufficient to force the oil along the oil feed passageway 110 and out through the outlets 124.
Optionally the crankshaft 100 has a direction of rotation in use, and the inlet 122 is shaped to draw in oil into the oil feed passageway 110 from the groove 118, and the outlets 124 are shaped to draw oil out of the oil feed passageway 110 into the bearing gaps between the crankshaft 100 and the plain bearing shells 112 to lubricate the bearings.
A need remains for a crankshaft for an engine lubrication arrangement having reduced numbers of oil feeding main journal bearings. Further, a need remains for a crankshaft for an engine lubrication arrangement requiring a reduced number of oil supply passageways provided in the engine block.
The Applicant has appreciated that a limitation upon the number of bearing shells that may each be adequately supplied with oil from an outlet 124 of an oil supply passageway 110 is the amount of oil that the oil supply passageway is able to deliver. In turn, the Applicant has also appreciated that a limitation upon the delivery of sufficient oil by the oil supply passageway is the pressure at which oil is provided to the inlet 122 of the oil supply passageway 110, throughout the rotation cycle of the crankshaft.
Accordingly a need remains in for an engine bearing arrangement in which oil is supplied to the inlet of an oil supply passageway 110 at higher pressures throughout the rotational cycle of a crankshaft than in known arrangements.